This invention relates generally to interlocking attachments for securing shims to backing plates, and in particular, to an improved interlocking attachment and method for ensuring improved mechanical attachment of the shim to the backing plate.
In a brake assembly, such as a disc brake assembly, a rotatable disc rotates with the axle of a wheel to be braked. Braking subassemblies, comprising a steel backing plate and a braking pad, may be disposed on opposite sides of the disc. As the subassemblies move inwardly under the force supplied by an actuated piston and a related caliper, the inner surfaces of the braking pads are engaged in frictional, braking contact with the disc. A high pitched and undesired brake squeal noise can be produced during such braking engagement of the pads on the disc, which may be produced by vibration of the subassemblies during braking actuation.
To reduce and/or to eliminate the undesired brake squeal noise, sound dampening shims have been used, both by original equipment manufacturers and by brake repair shops.
The sound dampening shim constructions are preferably positioned both between the actuated piston and the back surface of the related steel backing plate and also between the caliper and the back surface of its related steel backing plate.
Unfortunately, this frictional contact can cause a torque or twisting force on the shim by the related piston or caliper producing a shearing force in the adhesive of the shim. Under the extreme conditions of heat and vibration the adhesive by itself is not sufficient to prevent dislodging of the shim from the backing plate during braking.
The present inventors know of at least three embodiments to further reduce shifting of the shim during braking. The first is the use of tabs which may be provided at the edges of the shim. These tabs typically extend around the top edge of the backing plate and would assist in holding the shim in place. This arrangement however is less than satisfactory since the shim shape would have to closely match the shape of the backing plate in order for the tabs to align, thus leading to an enormous inventory to maintain complementary backing plates and shims.
An improved shim is commercially sold by the assignee of the present invention under the trademark DRIFTLOK™. A DRIFTLOK™ shim includes one or more extruded holes that align with corresponding aligned indentations in the back surface of the backing plate. Advantageously, all that is required is to ensure that each backing plate, no matter the size or shape, has the properly aligned indentations and enough surface area to support the shim. This construction yields a very desirable reduction on the shearing motion of the shim.
The present inventors however have discovered that still further improvements in the art are desirable. For example, a staple or other fastening device to further reduce or eliminate any shearing of the shim would be desirable. One such attempt at such a fastening device is described in U.S. Pat. No. 6,349,803. This patent describes the use of a retaining pin that is inserted into an opening in the shim and thereafter into an aligned hole in the backing plate. The shank of the retaining pin has outwardly projecting veins which are formed to a thread-type configuration prior to insertion of the pin into the opening in the backing plate. As described in the '803 patent, the insertion of the pin into the backing plate deforms the veins sufficiently so as to prevent the pin from screwing itself back out of the backing plate during the vibratory conditions occurring during braking operation of a disc brake assembly.
The inventors of the present invention believe that further advancements in the art are desirable. For example, one perceived disadvantage of the embodiment described in the '803 patent is the less than satisfactory coupling of the fastener to the backing plate due to the use of a predrilled hole in the backing plate. That is, as disclosed below, the use of a staple device that is driven into the backing plate causing the displacement of backing plate material into a trapped recessed region in the staple device, provides for an improved mechanical coupling arrangement between the shim and the backing plate.
The present inventors have recognized that such improvements to the state of the art are achievable. As such, the present invention overcomes the perceived deficiencies in the prior art as well as providing the objectives and advantages set forth above and below.